In the US, type 1 diabetes (T1D) impacts 1.3 million patients who exhibit increased morbidity and premature mortality due to renal, cardiovascular, ocular, and/or neurological complications. This T cell-mediated disease is noted by the autoimmune destruction of the insulin-producing b cells of the pancreatic islets leading to glycemic dysregulation. Although stimulation of immune regulatory pathways can successfully intervene to treat autoimmune diseases, current countermeasures for T1D mostly rely on insulin replacement therapies. Implementing a tolerogenic regimen still remains problematic for treating human autoimmune diseases. One alternative is to stimulate immune unresponsiveness in a bystander fashion without imposing global immunosuppression. Such an approach is particularly attractive since prior knowledge of the auto-Ag is not required and can be accomplished using an innocuous antigen, such as colonization factor antigen I (CFA/I) fimbriae from enterotoxigenic E. coli. Our past autoimmune studies have shown CFA/I fimbriae can establish an environment conducive to establishing disease-specific regulatory T cells (Tregs). When administered nasally or orally, CFA/I fimbriae mitigate experimental autoimmune diseases by inducing Tregs to produce IL-10 and TGF-b via the stimulation of IL-10-producing regulatory dendritic cells (DCs). To facilitate its eventual use in humans, a Lactococcus lactis strain expressing CFA/I fimbriae (Lactococcus-CFA/I) was generated and found to be superior to soluble fimbriae in conferring protection against autoimmune diseases. Lactococcus-based therapeutics has already been tested for treating autoimmune diseases in humans, and is generally regarded as safe. Given the success of this approach, the proposed studies will establish CFA/I fimbriae as the basis for a therapeutic for T1D. This will be accomplished by testing the hypothesis that CFA/I fimbriae promote a regulatory microenvironment upon interaction with tissue DCs, which in turn, activate T1D-specific Tregs to produce TGF-b, IL-10, and/or IL-35 which suppress or anergize pathogenic CD4+ and CD8+ T cells. To test this hypothesis, two Specific Aims are proposed. Studies in Specific Aim 1 will show that bystander immunity mediated by Lactococcus-CFA/I can prevent and stop T1D via disease-specific Tregs. Studies in Specific Aim 2 will determine mechanisms responsible for DCs and Tregs for conferring T1D protection. The impact of this work will discern whether these novel approaches in driving disease-specific Tregs can prevent further pancreatic islet destruction, and reduce the reliance on insulin replacement therapy.